How to Implement Secure Boot on NXP i.MX6ULL for Firmware Protection

Implementing Secure Boot on NXP i.MX6ULL to Prevent Unauthorized Firmware Execution

Secure Boot is a security standard that ensures only authorized firmware is executed during the startup process of a device. In this tutorial, we will walk through the steps to implement Secure Boot on the NXP i.MX6ULL processor. This process will help in preventing unauthorized firmware execution and enhance the security of your embedded system.

Prerequisites

• Basic knowledge of embedded systems and firmware development
• NXP i.MX6ULL development board
• Access to a computer with development tools installed
• Firmware image that you want to secure
• Code signing certificate
• OpenSSL or similar tool for signing

Parts/Tools

• NXP i.MX6ULL development board
• USB cable for power and data transfer
• SD card or eMMC storage for firmware
• Development environment (Linux preferred)
• OpenSSL for cryptographic operations

Steps

1. Prepare your firmware
   1. Compile your firmware code and generate the firmware image.
   2. Ensure the firmware image is in the correct format (e.g., .img or .bin).
2. Generate a code signing key
   1. Use OpenSSL to generate a private key and certificate.

   openssl req -new -x509 -days 365 -keyout private_key.pem -out certificate.pem

   2. Extract the public key for later use in verification.

   openssl rsa -in private_key.pem -pubout -out public_key.pem

3. Sign the firmware image
   1. Use OpenSSL to sign the firmware image.

   openssl dgst -sha256 -sign private_key.pem -out firmware.sig firmware.img

   2. Combine the firmware image and signature into a single file.

   cat firmware.img firmware.sig > firmware_signed.img

4. Load the signed firmware onto the device
   1. Transfer the signed firmware file to the SD card or eMMC storage.
   2. Ensure the device is configured to boot from the correct storage medium.
5. Configure the Secure Boot settings
   1. Access the bootloader configuration. Modify it to enable Secure Boot.
   2. Set the public key in the bootloader for verification of the firmware signature.
6. Test the Secure Boot process
   1. Power on the device and observe the boot process.
   2. Confirm that the device only boots with the signed firmware.

Troubleshooting

• Device does not boot
  • Check the bootloader configuration for any errors.
  • Ensure the signed firmware image is correctly formatted and transferred.
• Signature verification fails
  • Verify the public key is correctly loaded in the bootloader.
  • Ensure the firmware was signed with the corresponding private key.
• Unexpected behavior during boot
  • Check the firmware for bugs or compatibility issues with Secure Boot.
  • Review the serial console output for error messages.

Conclusion

Implementing Secure Boot on the NXP i.MX6ULL is a crucial step towards ensuring that your firmware is protected against unauthorized modifications. By following the steps outlined in this tutorial, you can secure your embedded system and mitigate the risks associated with firmware attacks. Regularly update your signing keys and firmware as part of maintaining device security.